docs: def add_suffix(file_path, suffix):
      """Adds suffix to a file name seperated by an underscore and returns file path."""
      split = os.path.basename(file_path).rsplit('.', 1)
      ext = split[1]
      name = split[0]
      out = str(name + '_' + suffix + '.' + ext)
      return os.path.join(os.path.dirname(file_path), out)